The present invention relates to a method of and an arrangement for reducing heat consumption of bottle cleaning machines with use of a heat pump, in which heat quantity supplied to the last spraying cell is partially withdrawn and supplied to one of pre-heating zones.
The heat pumps have been widely used in the field of bottle cleaning machines since certain time. It was proposed in particular to use dirty water discharged from the cleaning machine for the purpose of heat recovery, especially since this waste water has a relatively high temperature level on the one hand, and the determination of a predetrmined waste water discharge temperature during supplying into open network is mandatory by law on the other hand. With the use of a heat pump,lye solution flows at its hot side and the waste water of the cleaning machine flows at its cold side (Vortrag Brunnen-Fachgespraech, Nov. 30, 1981, Darmstadt).
In the case of the use of the discharging dirty water with respective high discharge temperature, the utilization of a heat pump is however efficient when a suitable heat quantity is withdrawn from the waste water. The temperatures must lower practically to the region of 10.degree. C.-15.degree. C. at the cold side of the heat pump, whereby a high temperature difference is produced between the cold side and the hot side. This high difference between the waste water end temperature and the lye solution end temperature at the hot side requires a respectively high compressor power with resulting such a low power figure of the use of heat pump which is considered as no economical. In connection with this,another approach was used in accordance with which water discharged from the first preheating device is cooled in a return cooling device by means of a heat exchanger, and added to the water, and the thus heated water of the return cooling device is cooled by means of a heat pump and again supplied to the return cooling device, while the liquid of the second pre-heating device is heated at the hot side of the heat pump.
This method is disclosed in the German document DE-OS No. 3,205,956. In accordance with the method disclosed in this document, first the waste water is cooled in the fresh water spraying zone and then supplied to the waste water channel. Here also,despite the connection of an exchanger which heats the spraying water, the temperature difference during subsequent flow through the heat pump is relatively high so that the above described disadvantages are not eliminated with this proposal as well. Moreover, in this known method a return cooling of the waste water is possible only to a small extent because of the high spraying water temperature and the pre-arranged spraying baths. Therefore, is is impossible to withdraw from the waste water the heat quantity which would be required for the purpose of an effective use of a heat pump. Moreover, in each cleaning machine there is a heat equilibrium between pre-cooling and return cooling zones so that the compressor power obtained in the proposed methods cannot be accommodated. This leads to the fact that a greater quantity of heat energy is supplied to the pre-heating bath (hot side), than can be taken and further supplied through the cage carriers, bottles and the like. As a result of this, undesirable heating process takes place which finally leads to turning off of the heat pump.
In accordance with another known method of cleaning bottles and the like disclosed in the German document DE-OS No. 2,510,927, a heat pump is arranged in a separate circuit and heat is withdrawn from the return cooling zone and directly supplied into the central lye solution bath. The basic goal of this method is to provide substantially complete fresh water economy. Thereby, practically the entire return cooling energy must be supplied in the heat pump. Under consideration of a bottle output temperature of 20.degree. C. proposed in this method, a spraying water temperature in the last zone is approximately 12.degree. C.-15.degree. C. In accordance with this, the heat pump operates with approximately 8.degree. C. at the cold side and with approximately 85.degree. C. at the hot side, including the required temperature drop in the heat exchangers. Therefore, as in the previously described methods, a relatively high temperature difference inside the heat pump circuit takes place with a resulting extremely low power figure of under 1.7 which with the conventional cooling means cannot be effective, Despite this, in this system with incorporation of the cooling load, a flow consumption of approximately 250 Kw is required in the event of a throughput in a bottle cleaning machine of approximtely 50,000 bottles per hour.